In recent years, a number of medical devices have been designed which are adapted for compression into a small size to facilitate introduction into a vascular passageway and which are subsequently expandable into contact with the walls of the passageway. These devices, among others, include blood clot filters which expand and are held in position by engagement with the inner wall of a vein, such as the vena cava. These vena cava filters are generally designed to remain in place permanently. Such filters include structure to anchor the filter in place within the vena cava, such as elongate diverging anchor members with hooked ends that penetrate the vessel wall and positively prevent migration in either direction longitudinally of the vessel. The hooks on filters of this type are rigid, and within two to six weeks after a filter of this type has been implanted, the endothelium layer grows over the diverging anchor members and positively locks the hooks in place. Now any attempt to remove the filter results in a risk of injury to or rupture of the vena cava.
A number of medical procedures subject the patient to a short term risk of pulmonary embolism which can be alleviated by a filter implant. In such cases, patients are often averse to receiving a permanent implant, for the risk of pulmonary embolism may disappear after a period of several weeks or months. However, most existing filters are not easily or safely removable after they have remained in place for more than two weeks, and consequently longer-term temporary filters that do not result in the likelihood of injury to the vessel wall upon removal are not available.
One potential problem with the known delivery device is that the filter (including the elongated pusher on which the filter is attached thereon) can be pulled backward (i.e., proximally) towards the user, which may result in the inadvertent separation of the pusher assembly and the filter within the delivery device.
Another potential problem that can arise during delivery of a filter results from the placement of various hooks in a delivery device which can lead to the hooks entangling or interfering with one another.